The present invention relates to a method for fabricating high-quality optical waveguide on a glass substrate.
Steady improvements have been made in optical fibers, light sources and light detectors with a view toward their practical application in the field of optical communications; and along with their development has been the further development of peripheral devices, such as light branching/coupling devices, optical switches and such other peripheral optical devices. Currently available optical devices, composed of such classic optical elements as lenses, reflectors, prisms and interference plates, are, however, disadvantageous as regards their size, mechanical stability, reliability and in other respects.
Research and development attempts have been made in many quarters, with an eye toward eliminating these disadvantages, as well as to work out optical integrated devices integrating a plurality of optical waveguide type elements on a single substrate.
Attempted methods to form an optical waveguide as a component part of such an optical integrated device, include the following. One method uses the polymerization of monomers in high polymer film (Takato et al., "Characteristics of high polymer light branching circuits, and their applications", Lecture Transcripts and Papers of the 1979 General National Convention of the Institute of Electronics and Communication Engineers of Japan, 4 (March 1979), 4-27 (in Japanese)). Another combines semiconductors of different materials ((Maehotoke et al., "Infrared optical waveguide made of non-crystalline semiconductors", Lecture Transcripts and Papers of the 1977 General National Convention (Commemorating its 60th Anniversary) of the Institute of Electronics and Communication Engineers of Japan, 4 (March 1977), 4-198 (in Japanese)). Still another method accumulates glass films uniformly on a glass substrate by the chemical vapour deposition (CVD) method and thereafter etches the glass films by the photolithography method (Mori et al., "Embedded type glass waveguide for optical circuit (DS guide)," Technical Research Report of the Institute of Electronics and Communication Engineers of Japan, OQE 80-135, (Feb. 20, 1981) pp. 57-64, (in Japanese)).
However, the method using high polymers is disadvantageous in that reliability decreases with age. In addition there are large optical transmission losses. The method utilizing semiconductors is handicapped by the large number of steps required for optical waveguide production and, again, great optical transmission losses are experienced. The process for forming an optical waveguide on a glass substrate by the CVD and photolithography methods is disadvantageous in that it takes many manhours.
Yet another method is disclosed in the U.S. Pat. No. 4,090,776, wherein an optical waveguide is produced by utilizing a laser beam. This method produces a waveguide formed on a glass substrate in the state of residual distortion, and may produce an unstable product.